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Dmitry [639]
3 years ago
9

A sample initially contains 8.0 moles of a radioactive isotope. How much of the sample remains after four half-lives? Express yo

ur answer using two significant figures.
Chemistry
1 answer:
Tju [1.3M]3 years ago
6 0

Answer:

0.50 mol

Explanation:

The half-life is <em>the time required for the amount of a radioactive isotope to decay to half that amount</em>.

Initially, there are 8.0 moles.

  • After 1 half-life, there remain 1/2 × 8.0 mol = 4.0 mol.
  • After 2 half-lives, there remain 1/2 × 4.0 mol = 2.0 mol.
  • After 3 half-lives, there remain 1/2 × 2.0 mol = 1.0 mol.
  • After 4 half-lives, there remain 1/2 × 1.0 mol = 0.50 mol.

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- Mole fraction:

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Explanation:

Hello,

- Molality: in this case, the solution is formed by 3.7% by mass of sodium chloride and water, thereby, we assume we have 100 g of solution in order to find the mass of sodium chloride as shown below:

m_{NaCl}=\frac{100g*3.7\%}{100\%} =3.7g

Hence, the moles of sodium chloride and kilograms of water are:

n_{NaCl}=\frac{3.7g}{58.45g/mol} =0.063molNaCl\\m_{H_2O}=100g-3.7g=96.3g*\frac{1kg}{1000g}=0.0963kgH_2O

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- Mole fraction: in this case, since we have previously computed the moles of sodium chloride, we now compute the moles of water as:

n_{H_2O}=\frac{96.3g}{18g/mol} =5.35molH_2O

Thus, the mole fraction of sodium chloride is:

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